Heteroblasty in Conchocarpus heterophyllus (A.St.-Hil.) Kallunki & Pirani (Rutaceae): An approach of leaf development from the unifoliolate leaves

Abstract

Heteroblasty is a phenomenon marked by abrupt changes in the development of organs of certain species. In our research on Conchocarpus heterophyllus, a shrub with palmately arranged leaflets ranging from 3(4) to 5(–7), we observed significant variations in leaf patterns between seedlings, young plants, and plants in the reproductive phase, indicating transition events during plant development. The focus of this study is to thoroughly investigate these events of heteroblasty and heterophylly in C. heterophyllus, with new evidence of the unifoliolate condition in Rutaceae. Morphological and anatomical observations were conducted from mature leaves of individuals at different stages of development. The results show that the heteroblasty in C. heterophyllus is marked by changes in leaf patterns across three stages. In stage 1, seedlings exclusively produce unifoliolate leaves from the first foliage leaf. After the eighth to tenth node from the cotyledons, heterophylly becomes evident with the emergence of leaves containing 2–3 leaflets, in addition to unifoliolate leaves, characterizing the second stage. The third stage is defined by the onset of the reproductive phase, marked by the presence of inflorescences. In this stage, the leaf complexity varies, with the number of leaflets ranging from 2 to 5, and unifoliolate leaves are lacking. Furthermore, our study identified the occurrence of vascular traces of leaflets in the swollen region located at the apex of the petiole of all unifoliolate leaves, occurring in stages 1 and 2. These vascular traces are interpreted as remnants of the lost lateral leaflets in unifoliolate leaves and represent novel evidence of this special condition in compound leaves. Heteroblasty in C. heterophyllus is a genetically controlled phenomenon, and consequently, prospective investigations involving microRNAs, particularly microRNAs 156 and 172, have the potential to provide valuable insights into the genetic mechanisms underlying the transition between different phases.